Glassed in Chain plates

[bigd14]

Different Approach

I have been pondering the question of what to do with my chainplates for many months now and I am slowly arriving at a solution. Instead of placing them externally, I am leaning towards replacing all six chainplates in the same deck location, but with a different configuration down below. This will preserve my pointing ability, which is highly desirable in a narrow waterway such as the Columbia River where the wind is often right on the nose.

This photo shows the current situation below decks. I exposed the horizontal strap that connects the three chainplates. This is the port side forward chainplate, and the strap extends off to the left (aft). I did this to see what the condition of the welds were and also to make way for the next step. The welds look fine, but there is lots of rust coming down from the deck area, so I am suspicious of the chainplates up there. They had been sitting in wet core material for years.

So here is the plan:

1. Cut off upright portion of chainplates at the crease shown in photos.
2. Drill 4 holes through hull at each chainplate. 2 of the holes will be through the existing metal strap (see diagram)
3. Build a pad at each chainplate area (or one big pad all the way across all 3) approximately 1 inch thick. Some combination of frp like G10 and biaxial cloth. Pad will extend up to the bottom of the deck and down as far as the bottom of the liner pan, and in towards the cabin far enough to allow the chainplate to mount flush against it and extend straight up through the existing deck exit slots.
4. Using holes already drilled on hull side, drill remainder of holes through pad.
5. Install SS backing plate on exterior of hull.
6. Install chainplate using 4 SS shoulder bolts.

Here is a photo of the proposed hole locations

Of course this brings up a bunch of questions and issues I'll need to consider:

Hull backing plate- necessary or not, and if so, what kind and size of material? I don't think it would look very good, but if it's necessary, I'm more concerned about structural soundness than looks.

Pad build up. Should I add a layer of frp, or just use layer upon layer of biax?

Individual pads, or one large one the entire length of the strap? I also thought about glassing in a strip of frp above the strap for its entire length to add strength. The upper bolt holes would go through this strip.

Liner issues. On the starboard side, the liner sits higher up than on the port. There is a void behind it which I will either have to fill with thickened epoxy somehow, or I will have to cut portions of it down. I don't want to leave a compressible space behind there. See photo below.

Sizing of through bolts and chainplates. I'll have to figure out existing rigging loads. The existing chainplate is 1/4 inch ss that is 1.5 inches wide. Right now I am thinking of upsizing everything a bit. 3/8 chainplates, 1/2" bolts perhaps. I like to overbuild stuff and I want the chainplates to be the strongest part of the rigging.

Here is a photo showing the liner issue. I could stuff the wire down between the hull and the inside liner that extends down to the starboard berth. Then there is the overhead liner glassed over this area. The liner is part of the structure of the boat so I don't want to try to take large sections of it out if possible. you can also see a void on each side of the chainplate area I cut out in the bolt hole photo above.

I see this being as strong or stronger than the original configuration, and will allow the chainplates to be removed and inspected periodically. The only weak spot I see would be the strap, which might still be subject to crevice corrosion if water were to get in. Of course I intend to properly seal all bolt holes and rebed them every so often to prevent this, so it shouldn't really be a problem for me.

Does this sound like a reasonable approach?

Thanks,

Doug

 

[PDX]

My thoughts

If I understand you right, you are installing what is essentially a fiberglass shim that matches the chainplate itself. The shim goes between the chainplate and the hull, therefore moving the chainplate inward whatever the thickness of the shim turn out to be. Is this right?

If so, my thought is, if the shim is thick enough you may not need a backing plate on the outside of the hull. The shim could serve as a backing plate itself. Just run the bolts all the way through the hull and cap them on the outside. You may be able to find cosmetically attractive nuts for the outside, something like an acorn only shallower. This would look a lot better than a rectangular chunk of SS bolted out there IMO. It would also be less of a corrosion magnet although I wonder if the torque on the nut would crack the gelcoat on the hull exterior.

I wish I had some advice on the headliner. On my boat it was not structural so the easiest thing to do with get rid of it.

 

[Emerald]

[snip]
If so, my thought is, if the shim is thick enough you may not need a backing plate on the outside of the hull. The shim could serve as a backing plate itself. Just run the bolts all the way through the hull and cap them on the outside. [snip]

I think I'm missing something here. Wouldn't you still have point loading on the hull where the bolt heads came through? I'm looking at the backing plate on the outside taking the load from the actual heads and distributing it over the area of the backing plate and across the hull at that point. Put it on the inside and you still just have the load on the bolt heads, I think....

 

[PDX]

Emerald

You might be right. But let me preface this response by saying I am not a structural engineer and that these are just my thoughts. Anyway, I'm assuming he intends to glass the shims into the hull because he mentions the possibility of doing a large built up glass area as an alternative to using prefab chunks of glass. If the shims are glassed into the hull you are effectively increasing the hull thickness by the shim thickness (plus adhesive glass thickness). Under that circumstance, wouldn't the loading on the hull (through the bolt tension) be all along the edges of the shims? You could spread the load further by giving the shims a larger surface area. On my boat, with glassed in chain plates, the tangs were built with outrigger tangs, presumably to spread the load on the hull.

 

[Emerald]

I'm not an engineer either, but have built enough stuff to have gotten a seat of the pants feel for what breaks and what doesn't. I agree, if the shims are bonded to the hull as one piece, it might very well be adequate. This is probably a good scenario where more is better. Use larger area shims than you would think necessary and build up more glass in a larger area spreading away from the actual chain plates to spread the load. Perhaps one of our resident engineers can chime in here. One of the things I've become sensitive to in general reinforcement is making sure you don't create a failure at the edge of what you reinforced. A very simple illustration of this is welding something together (that broke) without reinforcement to have it break right next to the weld down the road. I would think the key here is making sure the reinforcement is big enough to spread the load without causing a hard spot around the edges that takes the stress. I'm prone to over analyzing things, and I'm thinking out loud here, so take it all with a grain of sea salt

 

[bigd14]

Thanks for the replies PDX and David. PDX, you are correct I would essentially be creating a large shim out of layers of glass. I was also thinking of encapsulating a piece of G10 fiberglass board in between layers of glass to build thickness. I am also thinking now more seriously about extending the pad along and past all three chainplates on each side. So the ultimate depth of the hull+chainplate strap+new shim would be probably about 2 inches or more. If I can make sure I fill all voids, it should be a solid mass, and with the bolts in compression it all should act as a unit. I re-read this thread and it looks like John Kenan temporarily cut away the liner then re-glassed it in. If I did this I could extend the edges of the shim well down the hull using long fiberglass strips or sheets. It would not be continuous on the starboard side because of the bulkhead. But at least this would help spread loads even further.

As for bolts damaging the gelcoat, I would probably put the nuts on the inside, and I could very slightly countersink the gelcoat off the hull to assure no cracking. Or I could simply put a big backing plate on the exterior. It might not look quite right, but at least I know it would be solid, and reduce the point loading that Emerald is concerned about. While I want the boat to look good, I am most concerned about its structural integrity.

Thanks again for your comments.

Doug

 

[bigd14]

Update on Chainplate Issue

After much indecision I went ahead and cut the chainplates off. After realizing that there would not be enough room on the inside of the boat to install the new chainplates, I kind of had to go with external chainplates. So my wife and I came up with a design that we thought was attractive and would still be able to tie into the stainless steel strap embedded in the boat. It's wide at the base so it can span the old chainplate uprights.



Here is a photo of the mockup made of plywood. Also shows the slot where the chainplate was removed:

Here is how it will look installed:

I had our local boatyard metalworker help me drill the holes through the stainless strap. It worked pretty slick. The key was cutting fluid, lots of pressure (I drilled while he applied extra pressure using a long stick of wood as a lever for accessible holes and hand pressure for others), and a slow drill speed (150rpm). Went through a couple of pilot bits and two full sized bits for 12 holes, but otherwise no trouble.

Here are the materials used for drilling. The nice curls result from a slow speed and lots of pressure on the drill.

Here is a shot of the cutoff chainplates with all the holes drilled on the port side.

Next step is to glass a bunch of G10 backing plates into the inside, reinforce with bunch more glass over the top to bond it all together, then get new chainplates made.

 

[sproption]

Keep us posted!

Doug,

Please keep us posted...nice photos. I am very interested with how you do this and what it will look like.

Please let us know where things became difficult.

Great work.

Matt

 

[jkenan]

Hi Doug-

I see we're heading along the same path now. It does seem that once you make the decision to replace chainplates on the E27/E29, the only available option is to go with exterior plates due to space limitations with the liner. Even after cutting away my old chainplate tangs protruding through the decks, they were still darn near impossible to get out due to how they were bent. I couldn't imagine trying to get new ones in - especially since they'd have to be longer to fasten to the existing bar. The only real way to re-glass in new CP's is to gut the liner to provide access, which neither of us were willing to do given how that area interacts with bulkheads and how much work it would have been to rebuild.

I like your plan and design. You certainly can't go wrong with beefing up the interior with additional layup to spread the load. But I don't think it is all that necessary if you are using the old horizontal bar as a backing plate. FWIW, with my original exterior CP installment, I used two 1/2" bolts to fasten the CPs thru that bar as a backing plate. That was it, no addional layup or anything, just those two bolts. I had sailed it hard on a several occasions, and had one accidental jibe coming into Ocracoke at night that was powerful enough to break several of my mainsail luff slides (I got lucky there). Everything else held up fine. I'm not an engineer either, but I'd say that is some solid empirical support of the soundness of this design.

I highly recommend John Justin to fabricate your new plates - he been doing this for years for Pacific Seacraft, and his prices are quite reasonable. Contact me for his info if you like.

I'm finally getting ready to install my CP's, and launch. Will keep you posted, and hope you do the same.

 

[bigd14]

Hey John, I will definitely be contacting John Justin about fabbing up the CP's. Thanks for the source. I think I have his number from an earlier post or an IM or something. I have some final measurements to take and a few tweaks and then should be ready to move forward on it.

I drilled 7/16" holes through the straps, so I am committed to that size now. Given that the existing rigging is 3/16 and the toggle pins are 5/16 this should be more than adequate for the 27, especially since I will be adding a couple more bolts higher up (I wanted to minimize flexing of the CP's to prevent water ingress and also want a little margin of safety should one of the straps develop a crack).

Speaking of rigging size, what wire size are other E27 owners using? Is 3/16 the original spec?

One other note: I discovered some voids around the old chainplates. Try as I did to get thickened epoxy mashed all around them during the recore process, I apparently left some significant gaps, which would have allowed water to reach the core or somewhere else bad if the sealant were to fail. So going external will remove that particular issue.

I'll post another update soon.

Doug

 

[jkenan]

Doug-

Here are photos of John Justin's CP's. They are 1/4" 316SS, cut to spec's I provided. He had another job where the client had ordered his parts electropolished, so John threw mine into the batch at no extra cost. I don't have the shroud chainplates mounted yet, but you can see how I recessed the rubrail in those areas to allow for them.

Looking forward to seeing your progress!

John